#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int f(int x)
{
	if (x < 3)
		return 1;
	else
		return f(x - 1) + f(x - 2);
}
int main()
{
	int a = 0;
	scanf("%d", &a);
	printf("%d",f(a));
	return 0;
}